The authors describe three cases of perityphlitis secondary to Chlamydia trachomatis infection and revealed at laparotomy. Clinically, the symptoms invariably mimicked acute appendicitis. The pathogen was identified by a direct immunofluorescent assay with specific monoclonal antibodies (Microtrak). Prompt cure was achieved by doxycycline therapy. Thus, peroperatively, the discovery of an isolated perityphlitis with a normal appendix should raise the possibility of a C. trachomatis infection, even if there is no salpingitis.